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Ch.13 - Solutions
Chapter 13, Problem 118

Use the result of the previous problem to calculate the mole fraction of chloroform in the vapor above a solution obtained by three successive separations and condensations of the vapors above the original solution of carbon tetrachloride and chloroform. Show how this result explains the use of distillation as a separation method.

Verified step by step guidance
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insert step 1: Understand the concept of mole fraction and how it applies to vapor-liquid equilibrium. Mole fraction is the ratio of the number of moles of a component to the total number of moles in the mixture.
insert step 2: Recall Raoult's Law, which states that the partial vapor pressure of a component in a solution is equal to the mole fraction of the component in the liquid phase multiplied by the vapor pressure of the pure component.
insert step 3: Use the result from the previous problem to determine the initial mole fraction of chloroform in the vapor above the original solution. This will be your starting point for the first separation.
insert step 4: For each successive separation and condensation, apply Raoult's Law to calculate the new mole fraction of chloroform in the vapor. This involves using the mole fraction from the previous step as the new starting point.
insert step 5: Explain how the process of distillation, which involves repeated vaporization and condensation, increases the concentration of the more volatile component (chloroform) in the vapor phase, thus allowing for separation based on differences in volatility.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mole Fraction

Mole fraction is a way of expressing the concentration of a component in a mixture. It is defined as the ratio of the number of moles of a specific component to the total number of moles of all components in the mixture. This concept is crucial for understanding the composition of solutions and vapors, particularly in distillation processes where different substances are separated based on their volatilities.
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Mole Fraction Formula

Distillation

Distillation is a separation technique that relies on differences in boiling points to separate components of a liquid mixture. During distillation, the mixture is heated, causing the more volatile components to vaporize first. The vapor is then condensed back into liquid form, allowing for the collection of purified substances. This method is widely used in chemistry for separating liquids, such as chloroform from carbon tetrachloride.
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Vapor-Liquid Equilibrium

Vapor-liquid equilibrium refers to the state where the rate of evaporation of a liquid equals the rate of condensation of its vapor. This concept is essential in understanding how components behave in a distillation process, as it determines the composition of the vapor above a liquid mixture. The mole fraction of each component in the vapor can provide insights into the efficiency of separation achieved through distillation.
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Related Practice
Textbook Question

A solution of a nonvolatile solute in water has a boiling point of 375.3 K. Calculate the vapor pressure of water above this solution at 338 K. The vapor pressure of pure water at this temperature is 0.2467 atm.

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Textbook Question

The density of a 0.438 M solution of potassium chromate (K2CrO4) at 298 K is 1.063 g/mL. Calculate the vapor pressure of water above the solution. The vapor pressure of pure water at this temperature is 0.0313 atm. (Assume complete dissociation of the solute.)

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Textbook Question

The vapor pressure of carbon tetrachloride, CCl4, is 0.354 atm, and the vapor pressure of chloroform, CHCl3, is 0.526 atm at 316 K. A solution is prepared from equal masses of these two compounds at this temperature. Calculate the mole fraction of the chloroform in the vapor above the solution. If the vapor above the original solution is condensed and isolated into a separate flask, what will the vapor pressure of chloroform be above this new solution?

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Open Question
A solution of 49.0% H2SO4 by mass has a density of 1.39 g/cm³ at 293 K. A 25.0-cm³ sample of this solution is mixed with enough water to increase the volume of the solution to 99.8 cm³. Find the molarity of sulfuric acid in this solution.
Textbook Question

Find the mass of urea (CH4N2O) needed to prepare 50.0 g of a solution in water in which the mole fraction of urea is 0.0770.

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Textbook Question

A solution contains 10.05 g of unknown compound dissolved in 50.0 mL of water. (Assume a density of 1.00 g/mL for water.) The freezing point of the solution is -3.16 °C. The mass percent composition of the compound is 60.97% C, 11.94% H, and the rest is O. What is the molecular formula of the compound?

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